Hundreds of anti-abortion activists have gathered in the heart Belfast to protest at the opening of the first ever private abortion clinic on the island of Ireland.

In driving rain, the demonstrators said prayers and waved placards with graphic images of aborted foetuses at the entrance to the new Marie Stopes clinic on Great Victoria Street.

Some of them also tried to shout down a lone pro-choice demonstrator who held up her own placard with the words: "Been in the situation? Only then does your opinion count."

Danni Stanfield, a 21-year-old student from Belfast, said: "Many of the people here today, who are pro-life, if they were in that situation themselves they might take a different point of view. I don't think many here today have come from the background where they have gone through abortions themselves.

"I am pro-choice but I had to come here and support the clinic. I am not saying to women who got pregnant unplanned that they should have an abortion, but rather that they be allowed that choice."

She pointed out that the protesters have never been able to stop up to 1,000 women leaving Northern Ireland every year to have terminations in Britain. Northern Ireland is the only part of the UK where the 1967 Abortion Act does not apply owing to opposition from the political parties at Stormont and all the main churches.

There was a heavy police presence alongside the anti-abortion activists at the Marie Stopes clinic, which has offered services including terminations for women who are up to nine weeks pregnant. A smaller number of anti-abortion campaigners were also packed into the front of Belfast Opera House, directly across the road.

The clinic is based in the same building as the former Anglo Irish Bank, right in the heart of commercial Belfast.

A white van bearing the slogan "Abortion is Murder" was driven continuously around central Belfast as some passing motorists beeped their horns in support.

Ciara Coyle, who travelled from Derry to join the protest, said she believed abortion was wrong "no matter what the circumstances".

Asked how she and her fellow anti-abortion activists could stop the clinic from operating, Coyle replied: "Unfortunately all we can do is pray, to pray and to protest peacefully. To be in the streets. I just can't understand why our politicians and the likes of the health minister can't stop this already."

She denied that there was a demand among women within Northern Ireland for abortion services. "I do believe that Northern Ireland is a pro-life country, like the whole of Ireland, and we will continue to make our stand against this baby-killing clinic."

Meanwhile, Northern Ireland's attorney general has called for a Stormont investigation into the legality of the clinic's opening. John Larkin QC, chief law officer and adviser to the power-sharing government, said that while he cannot intervene he would be happy to give advice to the administration.

Among those attending the protest were individuals and groups from the Irish Republic, where there is an absolute ban on abortion. They fear that the opening of the clinic, which will provide medical and not surgical terminations, will allow women from south of the border to travel to Northern Ireland for abortions in certain circumstances.

Pro-choice campaigners plan to hold a rally in support of the Marie Stopes clinic on Thursday evening but intend to keep their distance from the anti-abortion activists.